This is an Omron E2EX5Y1M1OMS inductive proximity sensor from the E2E-X family. M18 cylindrical body, flush mount – you can bury it in a metal bracket or plate without false triggers from the surrounding steel. Senses ferrous targets at 5 mm, gives you a normally open (make contact) signal up to 264 V AC/DC, 300 mA load. Brassed housing, IP67-rated, so out here in the grease it'll take a hose-down.
If you're looking at the E2EX10MY12MOMS as an alternative, understand the trade-offs: that one is non-flush (senses 10 mm but needs clearance around the head) and comes with a 2 m cable pigtail. This E2EX5Y1M1OMS is flush mount and terminates via an M12 connector – no splice box required, plug and play. Same 300 mA, same brass housing, same IP67, same 29 mm hex on the barrel. Mounting style and wiring method are the real decision: if you've got a pre-drilled M18 hole with metal around it, flush mount is the one. If you need reach and can keep metal away, go non-flush.
M12 connector, 20–264 V AC/DC, 25 Hz, 5 mm, -25 to 70 °C.